Determining the fuel consumption and displaying it to the driver in motor vehicles are known. A process for determining the fuel consumption in motor vehicles is described for example in European Patent Application EP 1 205 738 A2. In this connection the fuel consumption is computed by means of the relative, indicated, instantaneous torque which can be delivered by the internal combustion engine, and a quantitative constant for the indicated torque and the output speed of the internal combustion engine and cylinder charge per revolution. Thus the total fuel consumption is determined with this process.
The fuel which is consumed in the motor vehicle is used however for various purposes. On the one hand, the fuel drives the engine which in turn can be used to propel the entire vehicle via the transmission, on the other hand however the generator is also driven by way of the engine. The generator supplies electrical consumers in the motor vehicle with the required voltage. These electrical consumers in a motor vehicle can be for example the air conditioning system or the rear window defroster. When these consumers are activated in a motor vehicle, that is to say, generally turned on the by driver, the generator must make available the required voltage and hence the fuel consumption of the vehicle increases.
By computing the total fuel consumption as is described for example in European Patent Application EP 1 205 738 A2, reliable determination of this additional fuel consumption cannot be ensured. In particular, in the process of the prior art it cannot be ensured that the driver will receive the information that the increased fuel consumption has been caused by the additionally activated electrical consumer and what amount this fuel increase has. Even if an increase in fuel consumption were recognized by the process of the prior art when an electrical consumer is turned on, and even if the driver were notified of this by the indication of a higher numerical value, it would not be apparent to the driver what caused this increase. In this context it must be considered in particular that the fuel consumption for producing the electrical energy for driving the electrical consumers is relatively low compared to the overall fuel consumption. A slight increase of the fuel consumption could therefore be overlooked by the driver or could possibly be attributed to another action, such as for example depressing the gas pedal.
Therefore the object of the invention is to make available a process with which during vehicle operation values for fuel consumption can be determined which accurately indicate the consumption which is caused by the electrical consumer. Furthermore, these values should be able to be made available to the vehicle driver in a suitable manner.